Radio-controlled model airplanes are sometimes used in flight research programs. When a model is used, a ground-based pilot sometimes tracks the model with binoculars and based on this information performs certain maneuvers with respect to the model. In addition to having the model in the field of view of the binoculars, the pilot also needs information about the model, such as, for example, angle of attack and airspeed for making his decisions. These decisions have to be made in a very short interval of time. Hence, it is necessary that the pilot view both the field of view of the binoculars and the information from the model at the same time. It is therefore the primary object of the invention to display in the field of view of binoculars numerical information about the object being viewed.
It is also important that the pilot be able to simultaneously see the field of view of the binoculars and the numerical information without refocusing his eyes. Thus, another object of the invention is to provide numerical information in the field of view of binoculars such that the user of the binoculars does not have to refocus his eyes in order to see both the field of view and the numerical information.